No abstract

Sensitive plant communities are complexes of species particularly susceptible to global environmental changes (climate, land use, etc.). In the temperate zone alpine areas are considered as the most important "hot spots" in this respect. In the Central Great Caucasus, which is the traditional alpine vegetation monitoring site in the Caucasus, on the basis of 50-years long (1964-2014) phytosociological and ecological studies the most sensitive plant communities were distinguished: 1) Treeline ecotone communities, including: (a) Evergreen prostrate shrubbery dominated by Rhododendron caucasicum, (b) Dwarf semi-shrubbery dominated by Dryas caucasica and (c)Thermo-hygrophilous subalpine tall herbaceous vegetation dominated by Heracleum sosnowskyi; 2) Subalpine broad-leaved mesophilous meadows dominated by Anemonastrum fasciculatum, Geranium ruprechtii, Betonica macrantha and Trollius ranunculinus; 3) Alpine carpet-like meadows ("Alpine carpets") consist of Campanula biebersteiniana, Veronica gentianoides, Taraxacum porphyrantum, Sibbaldia semiglabra, etc.; 4) Snow-bed vegetation (Galanthus platyphyllus, Fritillaria latifolia, etc.), and 5) Subnival/nival vegetation patches formed by 2-5(7) species (Cerastium kasbek, Alopecurus dasyanthus, Tripleurospermum subnivale, Saxifraga sibirica, S. flagellaris, Delphinium caucasicum, Nepeta supina, Pseudovesicaria digitata, Symphyoloma graveolens, etc.). Totally habitats of these plant communities cover about 1/3 of Kazbegi region area. Temperature rise, decrease in precipitation will lead to abrupt decrease of already small areas covered by Tertiary's relict tall herbaceous vegetation; elimination of a number of highly sensitive plant species including: relic, rare, endemic and critically endangered; disappearance of alpine snow-bed species. On account of early snow thawing or belated snowfall in autumn chionophyte plants (elfin, prostrate and dwarf shrubs and forbs in the alpine zone) sensitive to low moisture content, few and short-term snow cover and high temperature will lose. Probably sharp changes should be expected in subnival/nival zones, first of all, related to abrupt decrease in the glacier areas and subsequent increase in the distribution range of many species. According to the scenario suggested for the South Caucasus, which is based on predicted 3.9°C rise of temperature and decrease of precipitation by 9-13% during the century, it is expected that further climate warming may significantly change the vegetation and consequently the landscapes in the region. The vegetation may become similar to that of dry gorges of the Rocky Ridge of the Great Caucasus, which are situated 10-15 km to the north of the Kazbegi region.

Glaciers are a prominent feature in high mountains and can affect plant distribution along the gradients. However, the possible effect of glaciers on plant community structure at landscape scale has been little studied. We asked: if a glacier tongue crosses a slope laterally and potentially blocks dispersal and migrations, how can this affect vegetation structure and species composition below and above this barrier? A suitable study system is offered by slopes on Mt. Kazbegi, where we established a transect through the subnival and nival belts. We sampled vegetation below and above the glacier tongue and conducted direct gradient analyses to reveal possible effects of the glacier on patterns of species distribution and vegetation structure such as the ratio of solitary plants in vegetation patches. The obtained results indicate that the glacier tongue in our study does not cause a ?vegetation switch? in the usual sense of this phrase. However, it might contribute to an abrupt change in the share of solitary plants, as well as to a very rapid decline of plant abundance and species numbers above the glacier.